*{
    margin: 0;
    padding: 0;
    border: 0;
  }
  a{
    text-decoration: none;
  }
  
.back_top{
  position: fixed;
  bottom: 50px;
  right: 30px;
  background-color: rgb(158, 156, 156);
  width: 50px;
  height: 50px;
  line-height: 50px;
  cursor: pointer;
  margin-right: 80px;
  border-radius: 15%;
}
.back_top img{
  width: 50%;
  margin-left: 12px;
  margin-top: 8px;
  opacity: 0.5;
}
.back_top img:hover{
  opacity: 1;
}

